I'm sure if you put your mind to it you could probably find somewhere to shoe-horn in a bigger cooler. Find yourself a nice double-pass cooler.
I seem to remember seeing somewhere that someone had rotated the cooler 90 degrees on the vertical axis. (removed the scoop and pointed the cooler forward.)
Lastly, and I couldn't find it again, but there was a drag team out there that fitted a liquid cooling system onto the 1203. Replaced the cylinders and heads...